Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a first image in a sequence according to our design for a display screen or portion thereof with transitional graphical user interface;

FIG. 2 is a front view of a second image in the sequence thereof; and,

FIG. 3 is a front view of a third image in the sequence thereof.

The appearance of the transitional image transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another forms no part of the claimed design.

The long-dash broken lines showing a device, the medium-dash broken line showing the display screen or portion thereof, and all other broken lines showing portions of the graphical user interface, form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 